The present invention relates generally to the fields of athletic training, physical rehabilitation and evaluation, and physical activity monitoring, and more specifically to apparatus and methods of monitoring the orientation of body parts, measuring the range of motion of joints or limbs of the body, measuring levels of physical activity, and providing cuing and measurement feedback for training and rehabilitation purposes. The present invention also relates to hand-held devices for sensing the orientation and motion of body parts or other objects.
Athletic training systems and apparatus are known that may be employed to monitor the orientation or movement of a user's body as he or she engages in a particular sporting activity. For example, a conventional athletic training system may be attached to the user's head or any other suitable body part, and may include a number of tilt sensors for detecting the direction of tilt of the user's head relative to a user reference orientation (such as a “straight ahead” reference orientation) and/or to an adjustable tilt threshold magnitude. Such a conventional system may provide the user with one or more visible or audible indications of the orientation or movement of his or her body in real time. The user may employ the system to train his or her body to maintain a desired body posture or to execute a desired movement while performing a particular sporting activity. In addition, patients receiving physical therapy for balance disorders or other posture-related conditions may use the system to monitor their progress while performing rehabilitation exercises, or to monitor their posture as they go about their daily activities.
Although athletic training systems like the conventional system described above may be employed in various sporting and physical therapy applications, such systems have drawbacks. For example, in some conventional athletic training systems, the tilt sensors include accelerometers, which, because accelerometers are responsive to both acceleration and tilt, can generate misleading signals when the body part is accelerating. Further, when an accelerometer is used as a tilt sensor, the sensitivity and accuracy of the accelerometer are generally high when the sensitive axis of the accelerometer is close to horizontal, i.e., parallel to the earth's surface, but typically worsen as the sensitive axis of the accelerometer becomes vertical, i.e., perpendicular to the earth's surface. Moreover, it is often desirable to mount such athletic training systems in various orientations and/or on different parts of the user's body to suit a particular application and/or for aesthetic reasons. However, conventional athletic training systems typically require the sensitive axes of the tilt sensors to be precisely aligned relative to corresponding axes of the user. For example, when the system is attached to the user's headband, baseball helmet, or golf cap, the sensitive axis of one tilt sensor may have to be precisely aligned with the left/right axis of the user's head, while the sensitive axis of another tilt sensor may have to be precisely aligned with the front/back axis of the user's head. In addition, some users of conventional athletic training systems may be incapable of recognizing or responding to the visible or audible indications provided by the system. Alternatively, the type of visible or audible feedback provided by the conventional system may be insufficient in some applications, e.g., when an attending therapist requires quantitative feedback relating to the user's balance skill level, range of motion, conformance to a requested motion or sequence of motions, and/or in applications where users may require guidance or instruction from the training system itself in the absence of the trainer or therapist. The visible or audible feedback may also be inappropriate or unduly distracting to others, e.g., when the system is used in public places.
Athletic training systems are also known that employ tilt sensors in combination with one or more angular rate sensors such as gyroscopes for sensing and analyzing sequences of movement rather than just monitoring orientation. However, in addition to the drawbacks of conventional athletic training systems listed above, angular rate sensors can be more expensive and larger than accelerometers, can consume more power, and can exhibit significant drift errors.
Athletic training systems are also known that employ techniques to “arm” the system, i.e., to initiate monitoring activity based upon an analysis of user movement. To initiate the monitoring activity, they typically require the user to maintain a steady position for a specified time-period, which can lead to errors because the user can sometimes remain motionless with no intention of initiating the monitoring activity.
A number of systems for measuring the range of motion (ROM) of a body part about a joint or limb of the user's body are also known. For example, one such system that may be employed in physical rehabilitation applications includes a pair of accelerometers to compensate for the reduction in sensitivity and accuracy than can occur as the sensitive axis of a single accelerometer becomes vertical. The pair of accelerometers of this system needs to be aligned with the intended axis of rotation of the measured body part. In addition, to reduce the generation of erroneous or misleading signals when detecting the tilt of a body part that is undergoing acceleration, the system monitors the outputs of each accelerometer for either a varying signal or an over-range signal, which can be indicative of such acceleration.
However, the above-described conventional system for measuring range of motion also has drawbacks. For example, the acceleration of a body part can cause a distortion in the sensor reading that is not characterized by an over-range or varying signal output, and the system may be incapable of detecting such a condition. Further, the system must typically be manipulated while the measurements are being taken, for example, to trigger a reading when determining the initial orientation or maximum extension during range of motion (ROM) measurements. Moreover, the system must typically be repositioned to perform multiple measurements on a single joint to re-establish precise alignment of the sensors with each new axis of motion. As a result, it can be difficult to establish and/or maintain a precise alignment of the system with an axis and/or fulcrum of a joint or bone. Such alignment and re-alignment of the system may also interfere with or slow down the measurement process, thereby making the measurement process inaccurate, or painful for the user. In addition, when this system is used for diagnostic or physical rehabilitation purposes, the measurement process may interfere with the visual and/or tactile communication between a physical therapist and his or her patient, and/or an additional attendant may be required to take the actual measurement readings.
Another known system for monitoring physical activity may be employed in pedometers and other activity-monitoring devices. In such a system, the primary objective is to measure accurately the magnitude of an oscillating acceleration, such as an up-down acceleration of a runner or a front-back acceleration of a rower, which is subsequently used to estimate activity level and/or for other purposes. The system includes a plurality of accelerometers disposed in different directions. Signals generated by the accelerometers are compared, and, in response to the signal comparison, one of the accelerometers is selected as being aligned closest to the direction of user acceleration of interest. However, this system has drawbacks in that there is a practical limit to the number of accelerometers that may be employed in the system. Further, the likelihood that any one of the accelerometers will be oriented precisely in the direction of user acceleration may be low.
A number of hand-held devices for sensing motion are also known. For example, one such hand-held device includes a 2-axis accelerometer operative to control the position a graphical pointer on a display screen. To reduce undesirable pointer movements when responding to the tilt of the accelerometer as it also undergoes acceleration, the device filters out the DC and low frequency components of the accelerometer output, and inserts a new DC component in the system output with a slow feedback loop to maintain correspondence between the average tilt of the accelerometer and the center of the screen. One drawback of this device is that it does not provide a measurement of the actual magnitude of the accelerometer output. In addition, this device fails to address the reduction in sensitivity and accuracy than can occur as the sensitive axis of the accelerometer becomes vertical.
It would therefore be desirable to have improved apparatus and methods of sensing or monitoring body orientation and motion and measuring range of motion (ROM), for use in athletic training, physical rehabilitation and evaluation, and any other suitable physical activity or exercise. Such improved apparatus for sensing orientation and motion would avoid the drawbacks of the above-described conventional systems and apparatus. It would also be desirable to have an improved method of sensing orientation and motion that can be used in hand-held devices.